You must have access to a stove top, a potato ricer, a food processor, a microwave, and a kitchen scale.

Material Availability

Readily available

Cost

Low ($20 - $50)

Safety

This science project requires the use of a stove top, a knife, a food processor, and peelers. Minor injury is possible. You will be steaming the potatoes. Avoid placing any part of yourself in the path of the steam, as steam can cause painful burns. Adult supervision is required.

Abstract

What do you look forward to when the holidays arrive? Spending time with friends and family? Having lots of free time? How about the delicious food that comes out of the kitchen? You bet! What kinds of food do you have on your table during those special times of the year? For many people, mashed potatoes and gravy are usually on the holiday menu. Whether light and fluffy or smooth and silk-like, mashed potatoes are very satisfying. What is not satisfying is when the cook makes a mistake in preparing the mashed potatoes and ends up with a concoction that is lumpy and gluey. Yuck! So what is the best way to prepare mashed potatoes? Does it depend on the kind of potatoes you start with? Or how long you cook the potatoes? This science project will help you figure out the answers to these questions!

Objective

To determine the best way to make mashed potatoes with the best consistency.

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Introduction

Mashed potatoes, hash browns, French fries... Americans love potatoes! We eat approximately 140 pounds (lbs.) of potatoes per person each year. Germans eat about 200 lbs. of potatoes per person per year. That's a lot of spuds! Potatoes are a versatile food product. They can be fried, boiled, roasted, baked and steamed. Potatoes are definitely a nutritious food product. They are a fat-free and low-calorie product. A medium potato is about 100 calories and has 3 grams (g) of fiber, 4 g protein, 25 g of carbohydrates, and is high in vitamin C and potassium. Potatoes really pack a nutritional punch! Figure 1, below, shows a favorite way for people to enjoy their potatoes.

Potatoes are actually an ancient food. They were first cultivated 4,000–5,000 years ago in Peru. The natives of this region continued to develop many varieties of the potato. After the Spanish made contact with the Peruvian people, they brought the potato back to Spain. The plant then moved from Spain to the rest of Europe. It didn't gain approval right away, though. Europeans were suspicious of this new food plant; but by 1800, the potato was a familiar food item. In fact, the potato became the staple food of the Irish. Since it is easy to grow, most Irish were able to grow extra to feed their animals. When a potato disease hit Ireland in 1845, the main food crop was destroyed. This started a famine and led to about 1 million Irish dying, prompting many Irish to flee to the United States and Australia for a new start. The potato was planted in the United States as early as 1838 and there are now about 4,000 varieties of the potato!

Let's learn more about the internal cellular structure of the potato. Starch is the main component of the potato, making up about 75 percent of it. During growth, starch accumulates in the potato's cells in the form of granules. The starch granules are encased in a protein coat. Starch is the potato's reservoir, enabling new growth and allowing the potato plant to survive during the winter. Floury potatoes (like baking potatoes) have, on average, more starch than waxy potatoes (like thin-skinned red potatoes) do, which gives them a different density. If you look at a potato through a microscope, you will see that the cellular walls are made up of three components: cellulose,hemicellulose, and pectin. When potatoes are cooked, the hemicellulose in the cell walls break down, the cells separate, and the starch granules start to absorb water and expand. If you are baking a potato, the starch in the cells will absorb water that is already present in the cell. If you are boiling a potato, the starch will absorb some of the boiling water. Once the cell wall breaks open as a result of cooking and changes in temperature, some of the starch disperses from the cell. Floury potatoes behave differently than waxy potatoes because in floury potatoes the cells separate more easily and when they burst, release a larger number of starch granules. The consistency of the mashed potatoes depends upon how much starch has been released and how much water the starch has absorbed.

In this cooking and food science project, you will investigate the effect of cooking time and mashing method on the consistency of one type of potato (though you can also do your own consistency comparisons between different types in the Variations section at the bottom). You will work with russet (also called Idaho) potatoes, steam them for different times, and then use a potato ricer and a food processor to make the mash. Will one method result in better mashed potatoes than the other? Start cooking and find out!

Terms and Concepts

Calorie

Fiber

Protein

Carbohydrates

Vitamin C

Potassium

Cultivate

Cellular

Starch

Granule

Cellulose

Hemicellulose

Pectin

Parboil

Questions

Who is Antoine-Augustin Parmentier and what did he do for the potato?

From your research, why is it that people in the 1500s were not comfortable eating potatoes?

McGee, H. (2004, November 16). On Food and Cooking: The Science and Lore of the Kitchen. (pp. 302-304). New York: Scribner.

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Materials and Equipment

Stove top

Steamer basket or steamer pot with insert; available at your local department store or home goods store

Pot, big enough to hold the steamer basket (not needed if you have a steamer pot with steamer insert)

Potatoes, russet, 4.5-kilogram (kg) bag

Kitchen scale

Potato peeler

Cutting board

Knife

Timer, digital

Slotted spoon

Potato ricer; available at your local department store or home goods store

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Experimental Procedure

Introductory Notes: You will be comparing four cooking and mashing methods to see which one makes the best mashed potatoes. They are as follows:

Steam → Ricer → Fork mash

Steam → Food-processor mash

Parboil → Cool → Boil → Ricer → Food-processor mash

Parboil → Cool → Boil → Fork mash

Performing the Experiment

The first step in this science project is to steam the russet potatoes. Fill the pot with water. Place the steamer basket within the pot. The amount of water that you use depends upon the type of steamer that you are using. If you are using a steamer basket that sits inside the pot, then make sure that the water level will not touch the potatoes in the basket. If you are using a steamer pot with an insert, just fill the pot one-third of the way full. The water must not touch the potatoes during steaming.

Using the kitchen scale, weigh out 0.45 kg of potatoes. Quickly wash the potatoes to remove any loose dirt.

Carefully peel the potatoes with the potato peeler.

Place the steamer pot or the pot with the steamer basket on the stove top and start boiling the water. The potatoes should not be in the basket yet.

Cut the potatoes on the cutting board with the knife. Cut the potatoes into slices that are about 1 cm thick.

Once the water starts to boil and create steam, place the potato slices in the steamer. Make sure the water does not touch the potatoes. If it is, have an adult help you carefully pour some of the water out. Cover. Cooking the potato slices will take up to 10 minutes. Set the kitchen timer to 5 minutes and start steaming the potatoes. You want to steam the potatoes until a knife can easily pierce the potato slices.

Uncover the steamer after 5 minutes and pierce a potato slice through the middle with a knife. If the knife easily pierces the potato, then turn off the stove and remove the pot to a cold burner.

If it doesn't go through easily, then recover the pot and steam for another 5 minutes. Recheck the potato slices to see if they are done. If not, then steam for 1 minute and recheck to see if the potatoes are done. Continue this until the potatoes are just-done.

Add up the total steaming time and record this information in your lab notebook.

While you are cooking the potatoes, cut off 2 tablespoons (Tbsp.) from the stick of butter, place it on the microwave-safe plate and warm it in the microwave for just a few seconds. The butter should be softened, but not melted.

Once the potatoes are done, use the slotted spoon and take half of the potatoes from the steamer and place them into the ricer. Press the potato slices through the ricer into a bowl. Try to get all of the potatoes through the ricer.

Add 1 Tbsp. of softened butter to the warm potatoes and incorporate the butter into the potatoes with the fork. Keep mashing the potatoes until they become smooth. This should take 1–2 minutes. What do the potatoes look like? How do the potatoes feel with your fork as you incorporate the butter? Is it easy or difficult to get the fork through the potatoes? Use a spoon and take a bite. How do the potatoes feel in your mouth? Smooth and fluffy? Or gummy? Record your observations in your lab notebook. Rate this recipe on a scale of 1 to 3, where 1 yields lumpy and or gluey potatoes and 3 is a recipe that yields perfect mashed potatoes.Be sure to record the cooking method (steaming), the total time of steaming, and the method that you used to mash the cooked slices of potato. Cover the bowl with aluminum foil to keep the potatoes warm.

Attach the work bowl to the food processor base. Install the blade and plug in the food processor. Add the other half of the potatoes to the food processor and close the work bowl cover. Add the other 1 Tbsp. of softened butter to the warm potatoes in the food processor. Turn on the food processor and process the potatoes until they are smooth, about 15–20 seconds. What do the potatoes look like in the food processor? Use a fork to check the feel and consistency of the mash. Is it light and fluffy? Smooth? Gluey? Use a spoon and take a bite. How do the potatoes feel in your mouth? Smooth and fluffy? Or gummy? Record your observations in your lab notebook. Rate this recipe on a scale of 1 to 3, where 1 yields lumpy and or gluey potatoes and 3 is a recipe that yields perfect mashed potatoes.Be sure to record the cooking method (steaming), the total time of steaming, and the method that you used to mash the cooked slices of potato.

Use the spoon and remove the potatoes from the food processor and put them into a clean and unused bowl. Cover with aluminum foil to keep the potatoes warm. Clean the food processor bowl and blade. Dry and reassemble the food processor.

Now try a second method for cooking potatoes. Use the kitchen scale to weigh out 0.45 kg of potatoes.

Place the potatoes in the pot without the steamer basket or the steamer insert. Cover the potatoes with cool water and place the pot on a burner on the stove top. Parboil the potatoes at 140°F for 20 minutes. When you parboil the potatoes, you are cooking them briefly in water that is not quite boiling. Use a thermometer to make sure that the water is at the correct temperature. Once 20 minutes have elapsed, drain the potatoes. Use oven mitts to avoid burning your hands.

After draining the potatoes, immediately start running cold water over the potatoes while they are in the pot. Fill the pot with cold water and let the potatoes sit in the water for 5 minutes. After they are done soaking in the water, remove the potatoes from the water.

Drain the pot and put the potatoes back in. Cover the potatoes with water again. Place the pot back onto a burner and boil the potatoes for about 15 minutes (or until they are done) so that a knife can easily pierce the potatoes.

Once they are done cooking, drain the pot and remove the potatoes. Use oven mitts to handle the hot pot.

Let the potatoes cool down. In the meantime, soften 2 Tbsp. of butter in the microwave on a microwave-safe plate.

Peel the potatoes. To do this, hold the potatoes in a clean towel and quickly peel with your fingers. Put half of them into the food processor and set aside the other half. Add 1 Tbsp. of the softened butter to the potatoes in the food processor. Process the potatoes for 15 seconds, or until they are smooth. Stop the processor. What do the potatoes look like? Use a fork to check the feel and consistency of the mash. Is the consistency light and fluffy, smooth, gluey? Use a spoon and take a bite. How do the potatoes feel in your mouth? Smooth and fluffy or gummy? Record your observations in your lab notebook. Rate this recipe on a scale of 1 to 3, where 1 yields lumpy and or gluey potatoes and 3 is a recipe that yields perfect mashed potatoes. Be sure to record the cooking method (parboil, cool, boil), the total cooking time, and the method you used to mash the potatoes in your lab notebook. Use the spoon to remove the potatoes from the food processor into a clean bowl. Cover with aluminum foil to keep the potatoes warm.

After you have mashed the potatoes in the food processor, take the other half and put them through the potato ricer. Add 1 Tbsp. of the softened butter to the potatoes and incorporate into the mash with a fork. What do the potatoes look like? Use a fork to check the feel and consistency of the mash. Is the consistency light and fluffy? Smooth? Gluey? Use a spoon and take a bite. How do the potatoes feel in your mouth? Smooth and fluffy? Or gummy? Record your observations in your lab notebook. Rate this recipe on a scale of 1 to 3, where 1 yields lumpy and or gluey potatoes and 3 is a recipe that yields perfect mashed potatoes. Be sure to record the cooking method (parboil, cool, boil), the total cooking time, and the method you used to mash the potatoes in your lab notebook.

Repeat steps 1–21 two more times for a total of three trials. It is necessary to have three trials to ensure that your results are reproducible.

Analyzing Your Data

Compare the mashed potatoes that you made from the four methods. Does the cooking method matter? Is it better to use the ricer or the food processor? Which recipe produced the best mashed potatoes?

Make a data table in which you count which trials and recipes received a rating of 1, which trials and recipes received a rating of 2, and which trials and recipes received a rating of 3.

Plot the data you have collected on a bar graph. Label the x-axis Recipe Ratings (1, 2, 3) and the y-axis Number of Recipes with Each Rating. Assign each recipe a color so that you can keep track of the recipes. The bar graph will show how many times each recipe had a rating of 1, a rating of 2, and a rating of 3. For example, if the three trials of recipe 1 had one rating of 1 and two ratings of 3, then you would plot a bar at x=1 and two bars at x=3 (or one bar that is twice as long as the bar at x=1).

Does your plot clearly show a winning recipe?

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Variations

Repeat the experiment using red potatoes (which are waxy). Compare the consistency of the mashed potatoes made with red potatoes to the consistency of the mashed potatoes made with the russet potatoes.

How does increasing the cooking time when steaming the potatoes affect the feel and consistency of the resulting mash?

Compare mashed potatoes made by boiling potatoes until they are done, to the mashed potatoes made using the parboil method described above.

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Ask an Expert

The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

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